Signal transducers and activators of transcription (STAT) are pleiotropic transcription factors which mediate cytokine-stimulated gene expression in multiple cell populations (D. A. Levy, Cytokine Growth Factor Rev., 8:81 (1997)). All STAT proteins contain a DNA binding domain, a Src homology 2 (SH2) domain, and a transactivation domain necessary for transcriptional activation of target gene expression. Janus kinases (JAK), including JAK1, JAK2, Tyk, and JAK3, are cytoplasmic protein tyrosine kinases (PTKS) which play pivotal roles in initiation of cytokine-triggered signaling events by activating the cytoplasmic latent forms of STAT proteins via tyrosine phosphorylation on a specific tyrosine residue near the SH2 domain (See J. N. Ihle et al., Trends Genet., 11:69 (1995); J. E. Darnell et al., Science, 265: 1415 (1994); J. A. Johnston et al., Nature, 370:1513 (1994)). Tyrosine phosphorylated STAT proteins dimerize through specific reciprocal SH2-phosphotyrosine interactions and translocate from the cytoplasm to the nucleus where they stimulate the transcription of specific target genes by binding to response elements in their promoters (See W. J. Leonard, Nature Medicine, 2:968 (1996); Z. Zhong et al., PNAS USA, 91:4806 (1994) Darnell et al., Science, 264:1415 (1994)).
Among the four members of the JAK family, JAK3 is abundantly expressed in lymphoid cells and plays an important role in normal lymphocyte development and function, as evidenced by qualitative and quantitative deficiencies in the B-cell as well as T-cell compartments of the immune system of JAK3-deficient mice (T. Nosaka et al., Science, 270:800 (1995); D. C. Thomas et al., Science, 270:794 (1995)) and development of severe combined immunodeficiency in JAK3-deficient patients (R. H. Buckley et al., J. Pediatr., 130:379 (1997)). Besides lymphoid cells, non-lymphoid cells, including monocytes, megakaryocytes, endothelial cells, cancers cells, and, as descibed herein, mast cells also express JAK3, but no information is currently available regarding the physiologic function of JAK3 in these non-lymphoid cell populations. See, D. C. Thomas et al., Curr. Opit Immunol., 9:541 (1997); J. N. Hile, Philos. Trans. R. Soc. Lond B Biol. Sci, 351:159 (1996); J. W. Verbsky et al., J. Biol. Chem., 271:13976 (1996).
JAK-3 maps to human chromosome 19 p 12-13.1. A cluster of genes encoding protooncogenes and transcription factors is also located near this region. JAK-3 expression has been demonstrated in mature B-cells as well as B-cell precursors. JAK-3 has also been detected in leukemic B-cell precursors and lymphoma B-cells. The physiological roles for JAK-3 have been borne out through targeted gene disruption studies in mice, the genetic analysis of patients with severe combined immunodeficiency, and biochemical studies of JAK-3 in cell lines. A wide range of stimuli result in JAK-3 activation in B-cells, including interleukin 7 and interleukin 4. The B-cell marker CD40 constitutively associates with JAK-3 and ligation of CD40 results in JAK-3 activation, which has been shown to be mandatory for CD40-mediated gene expression. Constitutive activity of JAK-3 has been observed in v-abl transformed pre-B cells and coimmunoprecipitations show that v-abl physically associates with JAK-3, implicating JAK-3 in v-abl induced cellular transformation. See J. N. Ihle, Philos Trans R Soc Lond B Biol Sci, 351:159 (1996); W. J. Leonard et al., Cytokine Growth Factor Rev., 8:81 (1997); M. C. Riedy et al., Genomics, 37:57 (1996); M. G. Safford et al. [published erratum appears in Exp. Hematol., 1997 Jul;25(7):650] Exp. Hematol., 25:374 (1997); A. Kumar et al., Oncogene, 13:2009 (1996); S. M. Hoffman et al., Genomics, 43:109 (1997); P. J. Tortolani et al., J. Immunol., 155:5220 L (1995); N. Sharfe et al., Clin. Exp. Immunol., 108:552 (1997); C. B. Gurniak et al., Blood, 87:3151 (1996); C. Rolling et al., Oncogene, 10:1757 (1995); C. Rolling et al., FEBS Lett., 393:53 (1996); S. H. Hanissian et al., Immunity, 6:379 (1997); N. N. Daniel et al., Science, 269:1875 (1995).
Acute allergic reactions, also known as immediate (type I) hypersensitivity reactions, including anaphylaxis with a potentially fatal outcome, are triggered by three major classes of proinflammatory mediators, namely preformed, granule-associated bioactive amines (e.g., histamine, serotonin) and acid hydrolases (e.g., .beta.-hexosaminidase), newly synthesized arachidonic acid metabolites [e.g., leukotriene (LT) C.sub.4, prostaglandin D.sub.2, and platelet activating factor], and a number of proinflammatory vasoactive cytokines (e.g., tumor necrosis factor [TNF] .alpha., interleukin-6 [IL-6]) (R. Malavija et al., J. Biol. Chem., 268:4939 (1983); S. J. Galli et al., N. Eng. J. Med., 328:257 (1993)). These proinflammatory mediators are released from sensitized mast cells upon activation through the antigen-mediated crosslinking of their high affinity cell surface IgE receptors/Fc.epsilon.RI (M. J. Hamany et al., Cellular Signaling, 7:1535 (1995); A. M. Scharenberg et al., Clin. Immunol., G. Marone ed., Basel, Karger (1995) at p. 72)). IgE receptor/Fc.epsilon.RI is a multimeric receptor with .alpha., .beta., and homodimeric .gamma. chains (See U. Blank et al., Nature, 337, 187 (1989)). Both .beta.- and .gamma. subunits of the IgE receptor/Fc.epsilon.RI contain ITAMs (immunoreceptor Tyrosine-based Activation Motifs) which allow interaction with protein tyrosine kinases (PTK) and PTK substrates via their SH2 domains (See, N. Hirasawa et al., J. Biol. Chem., 270:10960 (1995)). The engagement of IgE receptors by antigen triggers a cascade of biochemical signal transduction events, including activation of multiple PTK (S. E. Lavens-Philips et al., Inflamm. Res., 47:137 (1998)). The activation of PTK and subsequent tyrosine phosphorylation of their downstream substrates have been implicated in the pathophysiology of type I hypersensitivity reactions (See K. Moriya et al., PNAS USA, 94:12539 (1997) Costello et al., Oncogene, 13:2595 (1996)).
Treatments for allergy are generally aimed at three possible components:1) avoidance or reduced exposure to the allergen, which can be very difficult especially in case of children; 2) allergen immunotherapy, which only works for some allergens, and which is frequently ineffective; and 3) pharnacotherapy (medication), which is the most effective treatment. Allergy medication either should prevent the release of allergy causing chemicals such as histamine from mast cells, or stop the response of histamine on the tissues. Most currently available medications are anti-histamines. Usually in case of allergy and asthma, doctors prescribe second generation anti-histamines such as loraitidine (Claratin.RTM.), fexofenidine (Allegra.RTM.) or leukotriene synthesis inhibitors such as zafirlukast (Accolate.RTM.) and zileutron (Zyflo.RTM.). Because the airway is more sensitive to leukotrienes produced by a number of inflammatory cells, anti-leukotriene agents are usually more effective for asthmatic conditions.
Although the second generation antihistamines are as effective as the older ones (Benadryl and Chlortrimeton) they have two potential problems. First, these drugs only counteract the effect of histamine released by mast cells in the body, which are responsible for many but not all the symptoms of allergy. Therefore, anti-histamines are very effective in decreasing the itching, sneezing, and nasal secretions, but do not provide relief from nasal stuffiness and late phase allergic reactions. A number of inflammatory mediators other than histamine, such as leukotrienes and a number of vasoactive cytokines, are also released by mast cells and basophils. These inflammatory mediators remain unaffected by anti-histamines and contribute significantly to the patho-physiology of allergy and asthma. Sometimes a combination of anti-allergic and inflammatory drugs works better, but at the same time these combinations cause adverse side effects. Secondly, in more severe allergic reactions (anaphylaxis), anti-histamines do not have therapeutic effect.
Until recently, therapy for asthma was based on the drug theophylline. This drug is an excellent, time proven, time tested drug but had numerous side effects. In the 1980's short acting beta-adrenergic compounds were introduced. In the 1990's asthma therapy shifted, so that asthmatic patients started taking cortocosteroids, cromolyn, and theophylline in different combinations. Recently three anti-leukotriene drugs:Accolate, Zyflo and Singulair, were introduced in to the U.S. market for the treatment of asthma. These medications either block the release of leukotrienes (Zylec) or block their effect on tissues (Accolate). Each is available in tablet form to be taken 2 to 4 times a day. Although leukotriene inhibitors do not inhibit early phase of allergy or asthmatic reaction, they are found to improve pulmonary function and asthma symptoms and significantly reduce requirement of beta-agonist by reducing the bronchial hyper-responsiveness.
Despite the above described advances in therapy, there is currently a need for therapeutic agents and methods that are useful for preventing or reducing immediate (type I) hypersensitivity reactions, including anaphylaxis and other allergic reactions.